1. Field of the Invention
This invention relates to a laminated coil for an eddy-current type strong alternating-current (AC) magnetic field generator which is suitable for various research works in magnetic properties of materials such as magneto-optics, in power magnetics, in bio-magnetics, and in nuclear fusion. More particularly, the invention relates to a laminated coil of the above type which is very simple in construction and is easy to manufacture.
2. Overview of the Invention
A laminated coil of the invention is for excitation of an AC magnetic field generator, and it has a plurality of annular conductor plates disposed one on the other, and each of the annular conductor plates has a radial slit. The slitted edge of each annular conductor is bent toward its adjacent annular conductor plate and connected thereto, so that a coil made of a continuous spiral conductor plate is formed by the annular conductor plates thus connected. One conductor disk with a central hole and a radial slit extending from the central hole is inserted into each of the inter-layer space between adjacent annular conductor plates of the coil, and the conductor disk is insulated from the annular conductor plates by inserting insulation rings between the opposite surfaces of the conductor disk and the facing annular conductor plates. Each insulation ring also has a radial slit. That slitted edge of each annular conductor plate which is bent toward and connected to the adjacent annular conductor plate extends through the radial slits of the conductor disk and the insulation ring.
When an alternating current flows through the laminated coil, an AC eddy current is induced in each conductor disk in its circumferential direction. The eddy current flows along the periphery of the conductor disk except its radial slit, and at the radial slit the eddy current flows along the slitted edge and the peripheral edge of the central hole of the conductor disk. Thus, the density of the eddy current becomes very high along the peripheral edge of the central hole, and a highly concentrated magnetic flux can be induced in the central hole of the conductor disk. In short, with the large AC exciting current, a strong AC magnetic field can be generated in the central hole of the conductor disk. The laminated coil of the above structure is characterized in that its impedance is very low, and a very large exciting current can be fed through it. Accordingly, a very high concentration of eddy currents can be produced along the edge of the central hole of each conductor disk, so that a strong AC magnetic field can be generated efficiently in the central hole. Further, the above-mentioned laminated coil is very easy to manufacture. Related Art Statement
Much efforts are currently undertaken for research and development of strong magnetic field generators by using large-scale experimental facilities, in order to promote investigations and studies of properties of materials in strong magnetic field, preparation and testing of new materials and experiments on nuclear fusion.
Conventional strong magnetic field generators can be classified into several groups; namely, destructive pulse strong magnetic field generators such as those of KNER method and the implosion method, nondestructive pulse strong magnetic field generators such as those of the multilayered coil type and the so-called MIT type, continuous strong magnetic field generators such as those of superconductive type and hybrid type.
The strong magnetic field generators of the prior art provide very strong magnetic fields, but they have shortcomings in that the duration of the strong magnetic fields generated is very short, that special facilities such as extremely low temperature apparatus and large power source apparatus are required, that only pulse or direct-current (DC) magnetic field can be generated, and that continuous generation of strong alternating-current (AC) magnetic field is not possible. On the other hand, the study of bio-magnetics has particularly advanced, and the need for investigation of the relation between the living body and AC magnetic field has increased, so that there is a demand for the development of a strong AC magnetic field generator.
To overcome the above shortcomings of the prior art, the inventors have disclosed a variety of strong AC magnetic field generators in their Japanese Patent Applications No. 57-25,517 and No. 61-228,459, and recently they have disclosed multilayered-eddy-current type strong AC magnetic field generators in their Japanese Patent Application No. 62-62,708 and No. 62-188,921. FIG. 4A and FIG. 4B show eddy-current type AC magnetic field generators which were disclosed by the inventors recently. When an AC current is fed into exciting coils of the magnetic field generator, eddy currents are induced in electric conductors which are magnetically coupled to the coils, and the conductors are connected to such a common central hole that the induced eddy currents are concentrated along the periphery of the central hole. Thereby, the AC magnetic flux density along the central hole is efficiently increased while minimizing the leakage flux.
More specifically, a conductor disk 11 of FIG. 4A has a central hole 12 and branch conductors 13a through 13d in the form of concentric cylindrical walls perpendicular to the plane of the disk 11. The conductor disk 11 of FIG. 4B is similar to that of FIG. 4A except that its branch conductors 13a through 13d are in the form of annular conductors parallel to the plane of the disk 11. In both examples of FIGS. 4A and 4B, the conductor disk 11 has a radial slit 14 extending from its central hole 12 to its periphery through all the branch conductors 13a through 13d. Exciting coils 15a through 15c are inserted in the three spaces between adjacent walls of the four branch conductors 13a through 13d as shown in the figures.
With an AC exciting current in each of the exciting coils 15a, 15b and 15c, an eddy current is induced in each of the branch conductors 13a, 13b, 13c and 13d in the circumferential direction thereof. Due to the presence of the radial slit 14, the path of the eddy current in each branch conductor is closed along the opposite edges of the radial slit 14 and the periphery of the central hole 12. Accordingly, the eddy currents of the individual branch conductors are all led to the periphery of the common central hole 12. Thus, a concentrated high magnetic flux is induced in the central hole 12, and it becomes possible to generate continuously a strong AC magnetic field within the central hole 12.
However, the multilayered-eddy-current type strong AC magnetic field generators which were proposed heretofore have the following shortcomings; namely, that they are difficult to manufacture because the conductor disk with branches has a complicated shape and the exciting coils consist of windings, and that the intensity of the magnetic field to be generated thereby is limited at a comparatively low level because the exciting coil of the proposed type inherently has a high inductance and the conductors of the proposed structure are inherently affected by surface effects. Thus, the multilayered eddy-current type strong AC magnetic field generators of the prior art still have serious problems to be solved.